Automobiles are currently being made lighter and more fuel efficient with each new product change. A vast majority of these products use a suspension system which employs passive components, that is, the components are fixed suspension members that use springs, rubber or other equivalent resilient members to damp the movements between the chassis and the ground engaging support. These components are called passive because they do not change in their nature to accommodate varying loading conditions of the vehicle, which include passengers, cargo and moving road conditions such as bumps or rolls. The design flexibility for such passive components to accommodate the increasing reduction of weight has about reached its limit. Engineers are new turning to actively controlled suspension systems where the components change their cushioning or resilient nature at each of the wheels in response to dynamic conditions.
One type of actively controlled suspension system employs air springs, which are air bags located at each of the support stations adjacent the wheels of the vehicle. The system typically has an air actuator to change the pressure in the air bags in response to a height sensing device which indicates the height of the vehicle on the air bags and the necessity for adjustment in air pressure.
Height adjusting devices, when used with an actively controlled suspension system, have been of the mechanical type such as illustrated in U.S. Pat. Nos. 2,929,640; 4,033,423 and 4,105,216.
What is needed is some kind of a height sensor that is responsive to a change in the curvature of the distensible members which comprise the air bags. Although wires have been embedded in compressible rubber members (such as in U.S. Pat. Nos. 3,277,256; 3,321,592; 3,920,940 and 3,710,050), none of these structures would be helpful with distensible air bag suspension systems because they do not operate in connection with a device that expands or stretches, only with a device that receives an outside force to compress the resilient member. Electrical wires have been embedded in rubber automotive tires to indicate a flat or blowout condition as shown in U.S. Pat. Nos. 3,593,269 and 2,033,424. However, these teachings fail to provide a device which again would operate effectively with an air bag suspension system having distensible members which form extreme curvatures to provide the suspension operation.